This is what you normally look at in your emails. The partial headers are the most important to your daily tasks. Such headers are the From Address, To Address, Subject, Date and Time, Reply To Address, CC, and BCC.
The full headers are simply more technical information than you normally see when you check your email. Sometimes we need those extra headers to solve a problem.
Here is a link which guides you to turn on Full Headers for whichever mail program you use: